As disclosed in for example JP 2014-175365A below, an on-board casing or the like that houses electrical devices employs a waterproof structure so that the electrical devices, which are accommodated therein, are prevented from breaking down due to water intrusion.
The approach of sealing the inside of the casing using a sealing member, as disclosed in JP 2014-175365A, increases manufacturing costs.
A problem to be solved by the present invention is to provide a substrate unit that has a simple structure and is able to prevent water that has entered the inside from reaching a mounting surface of the substrate.